diff --git a/vd960DBN/BLE/OnlyUpdateApp_Peripheral/APP/iot_mqtt_srv.c b/vd960DBN/BLE/OnlyUpdateApp_Peripheral/APP/iot_mqtt_srv.c
index f03016d..a083297 100644
--- a/vd960DBN/BLE/OnlyUpdateApp_Peripheral/APP/iot_mqtt_srv.c
+++ b/vd960DBN/BLE/OnlyUpdateApp_Peripheral/APP/iot_mqtt_srv.c
@@ -817,11 +817,11 @@ static void iot_send_heartbeat(void) {
     }
 
     snprintf(payload, sizeof(payload),
-        "{\"msg_id\":%d,\"cmd\":\"heartbeat\","
+        "{\"msg_id\":%lu,\"cmd\":\"heartbeat\","
         "\"ts\":%lu,\"data\":{"
         "\"uptime\":%lu,\"loop_status\":[%s,%s,%s,%s],"
         "\"net_status\":true,\"iot_status\":true}}",
-        ++g_iot_msg_id, dev_time_now(),
+        (unsigned long)(g_iot_msg_id + 1), dev_time_now(),
         mstick() / 1000,
         loop_ok[0] ? "true" : "false", loop_ok[1] ? "true" : "false",
         loop_ok[2] ? "true" : "false", loop_ok[3] ? "true" : "false");